[giomasce]

My problem with that question is that it seems to imply that of something has a very small probability to happen, then it cannot really happen. This is false. The probability of me generating my precise GPG or writing this exact comment were ridiculously small before these events happened, and still they happened.

Or, from another point of view, it's worthless to ask what is the probability of something that has already happened. Once something has happened (i.e., if you constrain to that thing having happened) its probability is one, full stop. You have to ask a question before running the experiment.

[eternalban]

That's not really correct. There are more bits of information regarding the event of your comment than the spell. It was observed you read the GP. Your profile is read, interests noted. Your comment history gives us probability of your making a comment today. All in all, pretty sure a much higher probability than "very small" in the sense that you intended it.